1. Field of the Invention
The present invention relates to a magnetic rotation transmitting device transmitting the rotation by an electric coupling, a hermetic stirring unit driving a stirring blade inside a hermetic container by the magnetic rotation transmitting device, and an electric furnace driving a pulling shaft of a single crystal or a crucible rotating shaft by using the magnetic rotation transmitting device.
2. Description of the Related Art
As a conventional magnetic rotation transmitting device transmitting a rotational motion from a drive side to a driven side by magnetically coupling permanent magnets in the drive side with permanent magnets in the side to be driven (driven side), the inventor has developed and proposed the one having a structure such that a right-and-left double pole magnet is used to one of the drive side and the driven side, and a both-surfaces double pole magnet is used to the other side (refer to Japanese Patent Application Laid-open No. 2678569).
Recently, a magnetic rotation transmitting device transmitting a large torque (the moment of power around a rotating shaft. A product obtained by multiplying a distance from the rotating shaft to a point of action of the force by a value of the force.) is required. In order to increase the transmitting torque in the conventional-type magnet rotation transmitting device described above, the size of respective magnets in the drive side and the driven side is required to be large, however, it is difficult to manufacture a large-sized permanent magnet having an uniform magnetic performance, and there exists a limit to allow the magnet to be large.